Artificial incoherent speckles enable precision astrometry and photometry in high-contrast imaging
Résumé
State-of-the-art coronagraphs employed on extreme adaptive optics enabled instruments are constantly improving the
contrast detection limit for companions at ever-closer separations from the host star. In order to constrain their
properties and, ultimately, compositions, it is important to precisely determine orbital parameters and contrasts with
respect to the stars they orbit. This can be difficult in the post-coronagraphic image plane, as by definition the central
star has been occulted by the coronagraph. We demonstrate the flexibility of utilizing the deformable mirror in the
adaptive optics system of the Subaru Coronagraphic Extreme Adaptive Optics system to generate a field of speckles
for the purposes of calibration. Speckles can be placed up to 22.5 λ/D from the star, with any position angle,
brightness, and abundance required. Most importantly, we show that a fast modulation of the added speckle phase,
between 0 and $\Pi$, during a long science integration renders these speckles effectively incoherent with the underlying
halo. We quantitatively show for the first time that this incoherence, in turn, increases the robustness and stability of
the adaptive speckles, which will improve the precision of astrometric and photometric calibration procedures. This
technique will be valuable for high-contrast imaging observations with imagers and integral field spectrographs alike.